Figure 4.

A fluorophore that reduces or increases its emission in the presence of the substrate can be used to monitor the changes inside the oocytes. Calcein reduces its emission intensity when interacting at physiological pH with divalent cations. Calcein-injected oocytes expressing the divalent metal transporter DMT1 (slc11a2) are incubated in a solution containing Me²⁺. It is possible to follow the fluorescence quenching by monitoring the decay of fluorescence intensity with a fluorescence microscope. It is also possible to measure the final fluorescence intensity in many oocytes at the same time, incubating them in solution with or without the Me²⁺, and measuring the fluorescence intensity of the supernatant obtained after the homogenization and centrifugation of the oocytes.